Modulation of transforming growth factor-β-induced kidney fibrosis by leucine-rich ⍺-2 glycoprotein-1

Revealing the multiple faces of LRG1: gene expression, structure, function, and therapeutic potential

BACKGROUND

As the structural characterization of the Leucine-rich alpha-2-glycoprotein 1 (LRG1) protein progresses, its functional diversity has been increasingly unveiled, highlighting its clinical relevance in elucidating disease pathogenesis and identifying potential therapeutic targets.

AIM OF REVIEW

Grounded in structural biology principles, this review systematically examines the regulatory mechanisms, pathological functions, and intervention strategies associated with LRG1, providing a theoretical foundation for translating these insights into clinical drug therapies.

KEY SCIENTIFIC CONCEPTS OF REVIEW

LRG1, distinguished by its leucine-rich repeat motifs, plays a pivotal role in various physiological and pathological processes. This review presents a comprehensive analysis of LRG1's multifaceted characteristics and its implications in disease. Initially, the regulatory mechanisms modulating LRG1 gene expression are detailed, encompassing both transcriptional and post-transcriptional controls. The structural attributes and distributions of LRG1 are subsequently outlined, with an emphasis on the functional relevance of its leucine-rich repeat motifs. Furthermore, the review elaborates on the molecular interactions through which LRG1 engages with distinct receptors, triggering downstream signaling pathways involved in pathological processes. Finally, current therapeutic approaches targeting LRG1 and its receptors are summarized, alongside prospective research avenues for innovative therapeutic development.

Mechanism of Astragaloside IV in Treatment of Renal Tubulointerstitial Fibrosis

Tubulointerstitial fibrosis (TIF) is one of the key indicators in evaluating the renal function of patients. Mild TIF can cause a vicious cycle of renal tubular glomerular injury and aggravate renal disease. Therefore, studying the mechanisms underlying TIF is essential to identify therapeutic targets, thereby protecting the renal function of patients with timely intervention. Astragaloside IV (AS-IV) is a Chinese medicine component that has been shown to inhibit the occurrence and progression of TIF via multiple pathways. Previous studies have reported that AS-IV protected against TIF by inhibiting inflammation, autophagy, endoplasmic reticulum stress, macrophages, and transforming growth factor-β1, which laid the foundation for the development of a new preventive and therapeutic option for TIF.

Isoquercitrin Alleviates Diabetic Nephropathy by Inhibiting STAT3 Phosphorylation and Dimerization

At the convergence point of multiple cytokine signals, signal transducer and activator of transcription 3 (STAT3) is a highly promising therapeutic target for diabetic nephropathy. Isoquercitrin, a natural small-molecule inhibitor of STAT3, may have beneficial effects on diabetic nephropathy; however, the underlying mechanism remains unclear. Isoquercitrin significantly mitigated renal inflammation and fibrosis by inhibiting STAT3 activity in mice with diabetic nephropathy. Moreover, STAT3 is a direct molecular target of isoquercitrin, which as corroborated by tight and stable noncovalent binding between them. This interaction is mechanistically supported by the affinity of isoquercitrin for the Ser668-Gln635-Gln633 region within the pY+1 binding pocket of the SH2 domain. This binding obstructs pivotal processes like STAT3 phosphorylation and dimerization, thereby suppressing its transcriptional function. Finally, a kidney-targeted nanocarrier, Iso@PEG-GK, is developed to load isoquercitrin, thus enhancing its therapeutic precision for diabetic nephropathy. Iso@PEG-GK significantly improved the absorption and renal distribution of isoquercitrin. This study is the first to demonstrate that isoquercitrin exerts a significant protective effect against diabetic nephropathy and may provide a novel therapeutic drug for this disease.

Endothelial RUNX3 controls LSEC dysfunction and angiocrine LRG1 signaling to prevent liver fibrosis

BACKGROUND AND AIMS

Liver fibrosis represents a global health burden, given the paucity of approved antifibrotic therapies. Liver sinusoidal endothelial cells (LSECs) play a major gatekeeping role in hepatic homeostasis and liver disease pathophysiology. In early tumorigenesis, runt-related transcription factor 3 (RUNX3) functions as a sentinel; however, its function in liver fibrosis in LSECs remains unclear. This study aimed to investigate the role of RUNX3 as an important regulator of the gatekeeping functions of LSECs and explore novel angiocrine regulators of liver fibrosis.

APPROACH AND RESULTS

Mice with endothelial Runx3 deficiency develop gradual and spontaneous liver fibrosis secondary to LSEC dysfunction, thereby more prone to liver injury. Mechanistic studies in human immortalized LSECs and mouse primary LSECs revealed that IL-6/JAK/STAT3 pathway activation was associated with LSEC dysfunction in the absence of RUNX3. Single-cell RNA sequencing and quantitative RT-PCR revealed that leucine-rich alpha-2-glycoprotein 1 ( LRG1 ) was highly expressed in RUNX3-deficient and dysfunctional LSECs. In in vitro and coculture experiments, RUNX3-depleted LSECs secreted LRG1, which activated HSCs throughTGFBR1-SMAD2/3 signaling in a paracrine manner. Furthermore, circulating LRG1 levels were elevated in mouse models of liver fibrosis and in patients with fatty liver and cirrhosis.

CONCLUSIONS

RUNX3 deficiency in the endothelium induces LSEC dysfunction, LRG1 secretion, and liver fibrosis progression. Therefore, endothelial RUNX3 is a crucial gatekeeping factor in LSECs, and profibrotic angiocrine LRG1 may be a novel target for combating liver fibrosis.

TRIM21 knockout alleviates renal fibrosis by promoting autophagic degradation of mature TGF-β1

Renal fibrosis is a common feature of chronic kidney disease, in which transforming growth factor-β1 (TGF-β1) plays an important role. Tripartite motif-containing 21 (TRIM21), an E3 ubiquitin ligase, has been studied for its role in acute kidney injury, but its role in renal fibrosis has not been reported. We analyzed public RNA-seq data of unilateral ureteral obstruction (UUO), ischemia-reperfusion injury (I/R), and aristolochic acid (AA)-induced renal fibrosis and found that TRIM21 expression was significantly elevated in fibrotic kidneys, which was verified by Western blot results corresponding to the mouse models. Similarly, TRIM21 expression was significantly elevated and negatively correlated with renal function in human fibrotic kidneys. We showed that TRIM21 knockout alleviated renal fibrosis in UUO mice. In vitro, TRIM21 knockout reduced TGF-β1-induced expression of mature TGF-β1 in HK-2 cells and primary renal tubular cells (PTECs), and this process was reversed by the autophagy inhibitor bafilomycin A1 (Baf-A1). Specifically, TRIM21 promoted K63-linked ubiquitination of p62, inhibited its oligomerization and thus its aggregation and segregation functions, and suppressed autophagic degradation of TGF-β1. Meanwhile, in the UUO mouse model, TRIM21 knockout promoted autophagy levels, and reduced the protein levels of mature TGF-β1 and the phosphorylation levels of SMAD2/3. In conclusion, our study demonstrates that TRIM21 knockdown alleviates renal fibrosis by promoting autophagic degradation of mature TGF-β1 and provides an insight into TRIM21 as a potential therapeutic target for the treatment of kidney fibrosis.

ADAMTS13 attenuates renal fibrosis by suppressing thrombospondin 1 mediated TGF-β1/Smad3 activation

Renal fibrosis is a common pathologic pathway for the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD). Its mechanisms are unclear and it lacks effective therapy. Thrombospondin 1 (TSP1) mediated transforming growth factor-β1 (TGF-β1) activation was confirmed to promote renal fibrosis. Recently, a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13 (ADAMTS13), was reported to inhibit Thrombospondin 1 (TSP1) mediated Ca2+ signaling in the myocardial cell, besides its cleavage of von Willebrand factor (VWF). Therefore, we hypothesized that ADAMTS13 might protect against renal fibrosis by inhibiting TSP1-mediated TGF-β1 activation. In this study, clinical data on renal fibrosis and healthy controls were collected. Renal fibrosis models were established both in vivo and in vitro. In vivo, mice underwent unilateral ureteral obstruction (UUO) for 14 days. In vitro, human proximal tubular epithelial cells (HK-2) were exposed to TGF-β1. The results showed that the expression of ADAMTS13 was decreased accompanied by the increased expression of TSP1 in patients with renal fibrosis and renal fibrosis models in vivo and in vitro. The administration of rhADAMTS13 reduced proteinuria and renal fibrosis in UUO mice. rhADAMTS13 inhibited the expression of TSP1 and the activation of TGF-β1/Smad signaling pathway. The knockdown of ADAMTS13 exhibited a contrary result. The regulation of TSP1 directly affected the protective role of ADAMTS13 in renal fibrosis. Moreover, rhADAMTS13 attenuated inflammation induced by UUO. In conclusion, ADAMTS13 attenuates renal fibrosis induced by UUO. ADAMTS13 exerts its protective role by inhibiting TGF-β1 /Smad signaling via TSP1. NEW AND NOTEWORTHY: ADAMTS13 may be used as a novel molecular marker and a new therapeutic target for renal fibrosis. In this paper, ADAMTS13 was found to have an antifibrotic effect independent of its cleavage of VWF.

METTL3 Potentiates M2 Macrophage-Driven MMT to Aggravate Renal Allograft Fibrosis via the TGF-β1/Smad3 Pathway

METTL3, a key enzyme in N6-methyladenosine (m6A) modification, plays a crucial role in the progression of renal fibrosis, particularly in chronic active renal allograft rejection (CAR). This study explored the mechanisms by which METTL3 promotes renal allograft fibrosis, focusing on its role in the macrophage-to-myofibroblast transition (MMT). Using a comprehensive experimental approach, including TGF-β1-induced MMT cell models, METTL3 conditional knockout (METTL3 KO) mice, and renal biopsy samples from patients with CAR, the study investigates the involvement of METTL3/Smad3 axis in driving MMT and renal fibrosis during the episodes of CAR. We found that elevated m6A modification and METTL3 levels strongly correlated with enhanced MMT and increased fibrotic severity. METTL3 knockout (METTL3 KO) significantly increased the m6A modification of Smad3, decreased Smad3 expression, and inhibited M2-driven MMT. Smad3 knockdown with siRNA (siSmad3) further inhibited M2-driven MMT, while Smad3 overexpression rescued the inhibitory effects of METTL3 silencing, restoring M2-driven MMT and fibrotic tissue damage. Additionally, the METTL3 inhibitor STM2457 effectively reversed M2-driven MMT and alleviated fibrotic tissue damage in CAR. These findings highlight that METTL3 enhances M2-driven MMT in renal fibrosis during CAR by promoting the TGF-β1/Smad3 axis, suggesting that METTL3 is a promising therapeutic target for mitigating renal fibrosis in CAR.

LRG1-Targeted Camptothecin Nanomicelles with Simultaneous Delivery of Olaparib for Enhanced Colorectal Cancer Chemotherapy

Camptothecin (CPT), an effective topoisomerase I inhibitor used in colorectal cancer chemotherapy, often faces limitations due to severe toxicities. Addressing this, we developed OCENM, a nanomedicine featuring the CPT-ET conjugate─comprising a cathepsin B-sensitive linker and CPT linked to the ET peptide targeting leucine-rich alpha-2-glycoprotein 1 (LRG1) and encapsulating Olaparib, a potent poly ADP-ribose polymerase (PARP) inhibitor. OCENM aims for precise CPT delivery to colorectal cancer sites overexpressing LRG1, while Olaparib disrupts compromised DNA repair pathways, enhancing DNA damage and promoting increased tumor cell apoptosis. Our results show OCENM accumulates preferentially in colorectal cancer models through LRG1 targeting and triggers synergistic tumor cell apoptosis through the dual action of enhanced DNA damage and inhibited repair mechanisms. This study not only highlights the potential of LRG1 as a strategic target for nanomedicine delivery but also underscores the therapeutic promise of combining CPT with Olaparib for colorectal cancer treatment.

Modulation of TGF-β signaling new approaches toward kidney disease and fibrosis therapy

The prevalence of chronic kidney disease (CKD) is increasing worldwide, posing a significant healthcare challenge. Despite the immense burden of CKD, optimal therapies remain limited in impact. Kidney fibrosis is a common mediator of all CKD progression, characterized by excessive extracellular matrix deposition and scarring of kidney parenchyma. Transforming growth factor-β (TGF-β) is a potent pro-fibrotic cytokine that signals through canonical and non-canonical pathways to promote kidney cell damage and fibrosis progression, thus garnering much interest as an optimal therapeutic target for CKD. However, the clinical translation of TGF-β inhibition in CKD and other disease settings has faced substantial challenges, particularly due to the highly pleiotropic effects of TGF-β in organ homeostasis and disease. Here, we review the kidney cell-specific biological effects of TGF-β signaling, discuss the current challenges in therapeutic targeting TGF-β in CKD, and provide the rationale for alternative targeting strategies of TGF-β signaling as potential approaches in CKD therapy. Selective inhibition of TGF-β signaling modulators to fine-tune TGF-β inhibition without a broad blockade may lead to new and safer treatments for CKD.

Apple Polyphenol Mitigates Diabetic Nephropathy via Attenuating Renal Dysfunction with Antioxidation in Streptozotocin-Induced Diabetic Rats

Diabetic nephropathy (DN) is a major cause of morbidity and mortality among patients with diabetes mellitus (DM). Studies have highlighted the critical role of reactive oxygen species (ROS) in the pathogenesis of DM and its complications. Apple polyphenol (AP) has demonstrated antioxidant properties in various models. In this study, we investigated the effects of AP on DN in a rat model. Type 1 diabetes was induced in Sprague-Dawley rats via a single intraperitoneal injection of streptozotocin (65 mg/kg) (n = 8). Rats with blood glucose levels exceeding 250 mg/dL were treated with AP at dosages of 0.5%, 1%, or 2% (w/w) in drinking water for 10 weeks. AP administration significantly improved early-stage DN markers, including reductions in the blood urea nitrogen-to-creatinine ratio and the urinary albumin-to-creatinine ratio (ACR), in a dose-dependent manner. AP treatment also significantly lowered blood triglyceride levels and reduced lipid peroxidation in kidney tissues. Histological analysis revealed that AP attenuated renal hydropic change, reduced glomerular basement membrane thickening, and restored mitochondrial morphology in diabetic rats. Additionally, the upregulation of transforming growth factor-beta (TGF-β) observed in the diabetic kidney was attenuated by AP treatment. In H2O2-stimulated rat mesangial cells, AP reduced ROS levels, accompanied by a reduction in TGF-β expression. These findings suggest that AP exerts protective effects against DN by improving renal function and mitigating oxidative stress, indicating its potential as a nutraceutical supplement for slowing DN progression.

Leucine-rich alpha-2-glycoprotein 1 deficiency suppresses ischemia-reperfusion injury-induced renal fibrosis

Ischemia reperfusion injury (IRI) is a major cause of acute kidney injury (AKI) and ultimately leads to renal fibrosis, primarily via the transforming growth factor-β (TGF-β) pathway. Leucine-rich alpha-2-glycoprotein 1 (LRG1), a novel modulator of the TGF-β pathway, has been implicated in the modulation of renal fibrosis by affecting the TGF-β/Smad3 signaling axis. However, the role of LRG1 in the transition from AKI to chronic kidney disease (CKD) remains unclear. This study aimed to investigate the functional role of LRG1 during the remodeling phase post-IRI. Unilateral IRI was induced in C57BL/6J wild-type (WT) mice and systemic LRG1 knockout (KO) mice. In C57BL/6J WT mice, renal LRG1 mRNA expression was significantly elevated on the ischemia/reperfusion side compared to the sham side over a 28-day period. In contrast, LRG1 KO mice demonstrated significantly reduced renal fibrosis compared to WT mice on postoperative day 28. Additionally, renal mRNA expression of TGF-β and associated pro-fibrotic genes was diminished in LRG1 KO mice compared to WT mice. Consequently, LRG1 KO mice exhibited attenuated IRI-induced chronic fibrosis. These findings indicate that LRG1 is involved in the pathogenesis of the transition from AKI to CKD and may be a potential therapeutic target.

Genome-wide CRISPR-based screen identifies E2F transcription factor 1 as a regulator and therapeutic target of aristolochic acid-induced nephrotoxicity

Aristolochic Acid I (AAI) is widely present in traditional Chinese medicines derived from the Aristolochia genus and is known to cause significant damage to renal tubular epithelial cells. Genome-wide screening has proven to be a powerful tool in identifying critical genes associated with the toxicity of exogenous substances. To identify undiscovered key genes involved in AAI-induced renal toxicity, a genome-wide CRISPR library screen was conducted in the human kidney-2 (HK-2) cell line. Among the altered sgRNAs, a significant enrichment of those targeting the E2F transcription factor 1 (E2F1) gene was observed in surviving HK-2 cells in the AAI-treated group. Interestingly, the role of E2F1 had not been previously explored in studies of AAI nephrotoxicity. Further investigations revealed that E2F1 promotes apoptosis by activating the p53 signaling pathway and upregulating pro-apoptotic genes, such as BAK and BAX. Additionally, using the high-throughput experiment- and reference-guided database of traditional Chinese medicine (HERB), cannabidiol (CBD) was identified as an inhibitor of E2F1 by suppressing the activity of NF-κB pathway. In vitro and in vivo models confirmed that CBD inhibits AAI-induced upregulation of E2F1, thereby suppressing p53-mediated apoptosis. In conclusion, this study highlights the crucial role of E2F1 in AAI-induced renal cell apoptosis and identifies CBD as a novel therapeutic candidate for mitigating AAI nephrotoxicity.

Development of a spontaneous model of renal interstitial fibrosis in NOD/SCID mice: Aging-induced pathogenesis

Renal interstitial fibrosis, a condition prevalent in aging humans and animals, is closely linked to the eventual development of renal failure. Establishing an animal model that exactly replicates the pathogenesis of renal interstitial fibrosis induced by natural aging in humans is crucial for advancing mechanistic studies and testing antifibrotic therapies. Implanted allogeneic or xenogeneic cells are cleared by the immune system when stem cell therapy is applied in nonimmunodeficient animal fibrosis models, affecting the effect of the intervention and making it difficult to demonstrate the survival, proliferation, differentiation, or secretion of the delivered autologous human-derived cells. This study effectively developed a model of spontaneous renal interstitial fibrosis linked to natural aging in 43-week-old NOD/SCID mice. Compared with those of 12- and 32-week-old mice, the kidneys of the model mice exhibited prominent fibrosis characteristics, accompanied by numerous fibrous septa and collagen deposition, increased COL1A1 expression, and decreased MMP9 expression. SA-β-gal activity and P21 gene expression levels increased, confirming renal cell senescence in the model mice. Additionally, an increase in α-SMA staining indicated an increase in epithelial-mesenchymal transition. More importantly, we observed TGF-β-SMAD3 pathway activation, mitochondrial dysfunction, decreased antioxidant capacity, oxidative stress, and an enhanced inflammatory response in the model group, consistent with renal interstitial fibrosis in elderly individuals. In this comprehensive investigation, we successfully developed a spontaneous mouse model of renal interstitial fibrosis and revealed the molecular pathways contributing to increased susceptibility to kidney injury and renal fibrosis in elderly individuals.

Therapeutic effect of total glucosides of paeony on IgA vasculitis nephritis: progress and prospects

IgA vasculitis nephritis (IgAVN), a type of immune system disease characterized by the deposition of IgA in the mesangial area of the glomerulus, is most common in children. Corticosteroids and immunosuppressants agents are commonly prescribed for the clinical management of IgAVN; however, these therapies are associated with numerous adverse reactions. This necessitates the discovery of alternative, potential therapeutic agents that can offer a safer treatment option. Natural plants contain abundant total glucosides of paeony (TGP), which represent one of the most prevalent secondary metabolites found within these organisms. TGP has been proven to be a safe and desirable natural medicine, with the most central ingredient being polyphenolic. TGP, a naturally occurring and cost-effective compound, exerts its therapeutic influence on IgAVN via diverse pathways and targets, with minimal side effects. Its substantial clinical potential underscores the importance of delving deeper into its pharmacological mechanisms, which hold great promise for novel drug development. This review examines the multifaceted therapeutic mechanisms of TGP in IgAVN encompassing modulation of Wnt/β-catenin pathways and programmed cell death pathways, antioxidant and anti-inflammatory effects, and enhancement of vascular repair. Additionally, we provide an overview of recent advancements in enhancing the bioavailability of TGP and highlight crucial considerations that may inform future research endeavors.

Exploring the Antifibrotic Mechanisms of Ghrelin: Modulating TGF-β Signalling in Organ Fibrosis

BACKGROUND

Fibrosis is a pathological condition that affects various organs by increasing fibrous connective tissue while reducing parenchymal cells. This imbalance can lead to compromised organ function and potential failure, posing significant health risks. The condition's complexity necessitates the exploration of effective treatments to mitigate its progression and adverse outcomes.

AIMS

This study aims to investigate the role of ghrelin, a peptide hormone known for its anti-inflammatory and anti-fibrotic properties, in modulating fibrosis across different organs. By binding to the growth hormone secretagogue receptor type 1a (GHSR-1a), ghrelin has shown potential in attenuating the fibrotic process, particularly through its interaction with the TGF-β signalling pathway.

METHODS

An extensive review of clinical and animal model studies focusing on liver, kidney, lung, and myocardial fibrosis was conducted. The primary focus was on examining how ghrelin influences the TGF-β signalling pathway, with an emphasis on the regulation of TGF-β expression and the suppression of Smad signalling molecules. The methodology involved analysing data from various studies to understand ghrelin's molecular mechanisms in combating fibrosis.

RESULTS

The findings from the reviewed studies indicate that ghrelin exerts significant anti-fibrotic effects across multiple organ systems. Specifically, ghrelin was found to downregulate TGF-β expression and suppress Smad signalling molecules, leading to a marked reduction in fibrous tissue accumulation and preservation of organ function. In liver fibrosis models, ghrelin reduced TGF-β1 levels and Smad3 phosphorylation, while in kidney and cardiac fibrosis, similar protective effects were observed. The data also suggest that ghrelin's effects are mediated through both canonical and non-canonical TGF-β pathways.

CONCLUSIONS

Ghrelin presents a promising therapeutic agent in the management of fibrosis due to its potent anti-inflammatory and anti-fibrotic actions. Its ability to modulate the TGF-β signalling pathway underscores a vital molecular mechanism through which ghrelin can mitigate fibrotic progression in various organs. Future research should focus on further elucidating ghrelin's molecular interactions and potential clinical applications in fibrosis treatment, offering new avenues for developing effective anti-fibrotic therapies.

Metabolic reprogramming and renal fibrosis: what role might Chinese medicine play?

Metabolic reprogramming is a pivotal biological process in which cellular metabolic patterns change to meet the energy demands of increased cell growth and proliferation. In this review, we explore metabolic reprogramming and its impact on fibrotic diseases, providing a detailed overview of the key processes involved in the metabolic reprogramming of renal fibrosis, including fatty acid decomposition and synthesis, glycolysis, and amino acid catabolism. In addition, we report that Chinese medicine ameliorates renal inflammation, oxidative stress, and apoptosis in chronic kidney disease by regulating metabolic processes, thereby inhibiting renal fibrosis. Furthermore, we reveal that multiple targets and signaling pathways contribute to the metabolic regulatory effects of Chinese medicine. In summary, this review aims to elucidate the mechanisms by which Chinese medicine inhibits renal fibrosis through the remodeling of renal cell metabolic processes, with the goal of discovering new therapeutic drugs for treating renal fibrosis.

Future of Uremic Toxin Management

During the progression of chronic kidney disease (CKD), the retention of uremic toxins plays a key role in the development of uremic syndrome. Knowledge about the nature and biological impact of uremic toxins has grown exponentially over the past decades. However, the science on reducing the concentration and effects of uremic toxins has not advanced in parallel. Additionally, the focus has remained for too long on dialysis strategies, which only benefit the small fraction of people with CKD who suffer from advanced kidney disease, whereas uremic toxicity effects are only partially prevented. This article reviews recent research on alternative methods to counteract uremic toxicity, emphasizing options that are also beneficial in the earlier stages of CKD, with a focus on both established methods and approaches which are still under investigation or at the experimental stage. We will consequently discuss the preservation of kidney function, the prevention of cardiovascular damage, gastro-intestinal interventions, including diet and biotics, and pharmacologic interventions. In the final part, we also review alternative options for extracorporeal uremic toxin removal. The future will reveal which of these options are valid for further development and evidence-based assessment, hopefully leading to a more sustainable treatment model for CKD than the current one.

m6A modification in non-coding RNAs: Mechanisms and potential therapeutic implications in fibrosis

N6-methyladenosine (m6A) is one of the most prevalent and reversible forms of RNA methylation, with increasing evidence indicating its critical role in numerous physiological and pathological processes. m6A catalyzes messenger RNA(mRNA) as well as regulatory non-coding RNAs (ncRNAs), such as microRNAs, long non-coding RNAs, and circular RNAs. This modification modulates ncRNA fate and cell functions in various bioprocesses, including ncRNA splicing, maturity, export, and stability. Key m6A regulators, including writers, erasers, and readers, have been reported to modify the ncRNAs involved in fibrogenesis. NcRNAs affect fibrosis progression by targeting m6A regulators. The interactions between m6A and ncRNAs can influence multiple cellular life activities. In this review, we discuss the impact of the interaction between m6A modifications and ncRNAs on the pathological mechanisms of fibrosis, revealing the possibility of these interactions as diagnostic markers and therapeutic targets in fibrosis.

Imperata cylindrica polysaccharide ameliorates intestinal dysbiosis and damage in hyperuricemic nephropathy

In this study, a combination of adenine and potassium oxonate was utilized to establish a hyperuricemic nephropathy (HN) mouse model, aiming to elucidate the effect through which Imperata Cylindrica polysaccharide (ICPC-a) ameliorates HN. In HN mice, an elevation in the abundance of Erysipelatoclostridium, Enterococcus, Prevotella, and Escherichia-Shigella was observed, whereas Lactobacillus and Bifidobacterium declined. Additionally, the systemic reductions in the levels of acetate, propionate, and butyrate, along with a significant increase in indole content, were noted. HN mice demonstrated intestinal barrier impairment, as evidenced by diminished mRNA expression of ZO-1, Occludin, and Claudin-1 and increased Mmp-9 levels. The pro-inflammatory factors IL-6, IL-17, TNF-α, IFN-γ, and COX-2 were overexpressed. Subsequent gavage intervention with ICPC-a markedly mitigated the inflammatory response and ameliorated colon tissue damage. ICPC-a effectively regulated the abundance of gut microbiota and their metabolites, including short-chain fatty acids (SCFAs), bile acids (BAs), and indole, promoting the correction of metabolic and gut microbiota imbalances in HN mice. These findings underscored the capacity of ICPC-a as a prebiotic to modulate gut microbiota and microbial metabolites, thereby exerting a multi-pathway and multi-targeted therapeutic effect on HN.

LRG1 loss effectively restrains glomerular TGF-β signaling to attenuate diabetic kidney disease

Transforming growth factor (TGF)-β signaling is a well-established pathogenic mediator of diabetic kidney disease (DKD). However, owing to its pleiotropic actions, its systemic blockade is not therapeutically optimal. The expression of TGF-β signaling regulators can substantially influence TGF-β's effects in a cell- or context-specific manner. Among these, leucine-rich α2-glycoprotein 1 (LRG1) is significantly increased in glomerular endothelial cells (GECs) in DKD. As LRG1 is a secreted molecule that can exert autocrine and paracrine effects, we examined the effects of LRG1 loss in kidney cells in diabetic OVE26 mice by single-cell transcriptomic analysis. Gene expression analysis confirmed a predominant expression of Lrg1 in GECs, which further increased in diabetic kidneys. Loss of Lrg1 led to the reversal of angiogenic and TGF-β-induced gene expression in GECs, which were associated with DKD attenuation. Notably, Lrg1 loss also mitigated the increased TGF-β-mediated gene expression in both podocytes and mesangial cells in diabetic mice, indicating that GEC-derived LRG1 potentiates TGF-β signaling in glomerular cells in an autocrine and paracrine manner. Indeed, a significant reduction in phospho-Smad proteins was observed in the glomerular cells of OVE26 mice with LRG1 loss. These results indicate that specific antagonisms of LRG1 may be an effective approach to curb the hyperactive glomerular TGF-β signaling to attenuate DKD.

LRG1-Targeted Nintedanib Delivery for Enhanced Renal Fibrosis Mitigation

Renal fibrosis lacks effective nephroprotective drugs in clinical settings due to poor accumulation of therapeutic agents in damaged kidneys, underscoring the urgent need for advanced renal-targeted delivery systems. Herein, we exploited the significantly increased expression of the leucine-rich α-2 glycoprotein 1 (LRG1) protein during renal fibrosis to develop a novel drug delivery system. Our engineered nanocarrier, DENNM, preferentially targets fibrotic kidneys via the decorated ET peptide's high affinity for LRG1. Once internalized by damaged renal cells, DENNM releases its encapsulated nintedanib, triggered by the active caspase-3 protease, disrupting the nanomedicine's structural integrity. The released nintedanib effectively reduces the level of expression of the extracellular matrix and impedes the progression of renal fibrosis by inhibiting the transforming growth factor-β (TGF-β)-Smad2/3 pathway. Our comprehensive in vitro and in vivo studies validate DENNM's antifibrotic efficacy, emphasizing LRG1's potential in renal targeted drug delivery and introducing an innovative approach to nanomedicine for treating renal fibrosis.

The role of intercellular communication in diabetic nephropathy

Diabetic nephropathy, a common and severe complication of diabetes, is the leading cause of end-stage renal disease, ultimately leading to renal failure and significantly affecting the prognosis and lives of diabetics worldwide. However, the complexity of its developmental mechanisms makes treating diabetic nephropathy a challenging task, necessitating the search for improved therapeutic targets. Intercellular communication underlies the direct and indirect influence and interaction among various cells within a tissue. Recently, studies have shown that beyond traditional communication methods, tunnel nanotubes, exosomes, filopodial tip vesicles, and the fibrogenic niche can influence pathophysiological changes in diabetic nephropathy by disrupting intercellular communication. Therefore, this paper aims to review the varied roles of intercellular communication in diabetic nephropathy, focusing on recent advances in this area.

Targeted degradation of LRG1 to attenuate renal fibrosis

Leucine-rich α-2 glycoprotein 1 (LRG1), a secreted glycoprotein, has been identified as significantly upregulated in renal fibrosis, potentially exacerbating the condition by enhancing TGF-β-Smad3-dependent signaling pathways. Herein, utilizing our developed LRG1-targeting peptide for LRG1 recruitment and lenalidomide for E3 ubiquitin ligase engagement, we developed an advanced proteolysis targeting chimera, ETTAC-2, specifically designed for LRG1 degradation. Our cellular degradation assays validated that ETTAC-2 effectively degraded LRG1 through a proteasome-dependent mechanism, achieving half-maximal degradation at a concentration of 8.38 µM. Furthermore, anti-fibrotic experiments conducted both in vitro and in vivo revealed that ETTAC-2 efficiently induced LRG1 degradation in fibrotic kidneys. This action effectively inhibited the TGF-β-Smad3 signaling pathway and diminished the secretion of fibrosis-associated proteins, consequently attenuating the progression of renal fibrosis. Our study highlights the pivotal role of LRG1 in renal fibrosis and positions ETTAC-2 as a promising therapeutic candidate for targeted LRG1 intervention.

Leucine rich α2 glycoprotein 1 derived from malignant pleural mesothelioma cells facilitates macrophage M2 phenotypes

Background: Macrophages constitute the main part of infiltrating immune cells in Malignant pleural mesothelioma (MPM) and abnormally high ratios of M2 macrophages are present in both pleural effusion and tissue samples of MPM patients. Whether MPM cells affect formation of M2 macrophages is poorly understood. In this study, we focused on identification of MPM-cells-derived soluble factors with M2-promoting effects. Methods: Media of malignant pleural mesothelioma cells were collected and soluble factors affecting macrophages were analyzed by mass spectrometry. TGF-β receptor inhibitor SB431542 was used as the entry point to explore the downstream mechanism of action by qRT-PCR, WB and immunofluorescence. Results: The serum-free culture media collected from the human MPM cells Meso1 and Meso2 significantly enhanced expression of the M2 signature molecules including IL-10, TGF-β and CD206 in the human macrophages THP-1, while the culture medium of the human MPM cells H2452 did not show such M2-promoting effects. Analysis of proteins by mass spectrometry and ELISA suggested that Leucine rich α2 glycoprotein 1(LRG1) was a potential candidate. LRG1 time- and dose-dependently increased expression of the M2 signature molecules, confirming its M2-promoting effects. Furthermore, LRG1's M2-promoting effects were reduced by the TGF-β receptor inhibitor SB431542, and LRG1 increased phosphorylation of Smad2, indicating that M2-promoting effects of LRG1 were via the TGF-β receptor/Smad2 signaling pathway. Conclusions: Our results provide a potential M2-promoting new member, LRG1, which contributes to the immune escape of MPM via the TGF-β receptor/Smad2 signaling pathway.

Proteomic, single-cell and bulk transcriptomic analysis of plasma and tumor tissues unveil core proteins in response to anti-PD-L1 immunotherapy in triple negative breast cancer

BACKGROUND

Anti-PD-1/PD-L1 treatment has achieved durable responses in TNBC patients, whereas a fraction of them showed non-sensitivity to the treatment and the mechanism is still unclear.

METHODS

Pre- and post-treatment plasma samples from triple negative breast cancer (TNBC) patients treated with immunotherapy were measured by tandem mass tag (TMT) mass spectrometry. Public proteome data of lung cancer and melanoma treated with immunotherapy were employed to validate the findings. Blood and tissue single-cell RNA sequencing (scRNA-seq) data of TNBC patients treated with or without immunotherapy were analyzed to identify the derivations of plasma proteins. RNA-seq data from IMvigor210 and other cancer types were used to validate plasma proteins in predicting response to immunotherapy.

RESULTS

A random forest model constructed by FAP, LRG1, LBP and COMP could well predict the response to immunotherapy. The activation of complement cascade was observed in responders, whereas FAP and COMP showed a higher abundance in non-responders and negative correlated with the activation of complements. scRNA-seq and bulk RNA-seq analysis suggested that FAP, COMP and complements were derived from fibroblasts of tumor tissues.

CONCLUSIONS

We constructe an effective plasma proteomic model in predicting response to immunotherapy, and find that FAP+ and COMP+ fibroblasts are potential targets for reversing immunotherapy resistance.

LRG1 Contributes to the Pathogenesis of Multiple Kidney Diseases: A Comprehensive Review

Background

The increasing prevalence of kidney diseases has become a significant public health issue, with a global prevalence exceeding 10%. In order to accurately identify biochemical changes and treatment outcomes associated with kidney diseases, novel methods targeting specific genes have been discovered. Among these genes, leucine-rich α-2 glycoprotein 1 (LRG1) has been identified to function as a multifunctional pathogenic signaling molecule in multiple diseases, including kidney diseases. This study aims to provide a comprehensive overview of the current evidence regarding the roles of LRG1 in different types of kidney diseases.

Summary

Based on a comprehensive review, it was found that LRG1 was upregulated in the urine, serum, or renal tissues of patients or experimental animal models with multiple kidney diseases, such as diabetic nephropathy, kidney injury, IgA nephropathy, chronic kidney diseases, clear cell renal cell carcinoma, end-stage renal disease, canine leishmaniosis-induced kidney disease, kidney fibrosis, and aristolochic acid nephropathy. Mechanistically, the role of LRG1 in kidney diseases is believed to be detrimental, potentially through its regulation of various genes and signaling cascades, i.e., fibronectin 1, GPR56, vascular endothelial growth factor (VEGF), VEGFR-2, death receptor 5, GDF15, HIF-1α, SPP1, activin receptor-like kinase 1-Smad1/5/8, NLRP3-IL-1b, and transforming growth factor β pathway.

Key Messages

Further research is needed to fully comprehend the molecular mechanisms by which LRG1 contributes to the pathogenesis and pathophysiology of kidney diseases. It is anticipated that targeted treatments focusing on LRG1 will be utilized in clinical trials and implemented in clinical practice in the future.

Low dose cadmium inhibits syndecan-4 expression in glycocalyx of glomerular endothelial cells

Cadmium (Cd) is one of the most polluting heavy metal in the environment. Cd exposure has been elucidated to cause dysfunction of the glomerular filtration barrier (GFB). However, the underlying mechanism remains unclear. C57BL/6J male mice were administered with 2.28 mg/kg cadmium chloride (CdCl2) dissolved in distilled water by oral gavage for 14 days. The expression of SDC4 in the kidney tissues was detected. Human renal glomerular endothelial cells (HRGECs) were exposed to varying concentrations of CdCl2 for 24 h. The mRNA levels of SDC4, along with matrix metalloproteinase (MMP)-2 and 9, were analyzed by quantitative PCR. Additionally, the protein expression levels of SDC4, MMP-2/9, and both total and phosphorylated forms of Smad2/3 (P-Smad2/3) were detected by western blot. The extravasation rate of fluorescein isothiocyanate-dextran through the Transwell was used to evaluate the permeability of HRGECs. SB431542 was used as an inhibitor of transforming growth factor (TGF)-β signaling pathway to further investigate the role of TGF-β. Cd reduced SDC4 expression in both mouse kidney tissues and HRGECs. In addition, Cd exposure increased permeability and upregulated P-Smad2/3 levels in HRGECs. SB431542 treatment inhibited the phosphorylation of Smad2/3, Cd-induced SDC4 downregulation, and hyperpermeability. MMP-2/9 levels increased by Cd exposure was also blocked by SB431542, demonstrating the involvement of TGF-β/Smad pathway in low-dose Cd-induced SDC4 reduction in HRGECs. Given that SDC4 is an essential component of glycocalyx, protection or repair of endothelial glycocalyx is a potential strategy for preventing or treating kidney diseases associated with environmental Cd exposure.

The disruptive role of LRG1 on the vasculature and perivascular microenvironment

The establishment of new blood vessels, and their subsequent stabilization, is a critical process that facilitates tissue growth and organ development. Once established, vessels need to diversify to meet the specific needs of the local tissue and to maintain homeostasis. These processes are tightly regulated and fundamental to normal vessel and tissue function. The mechanisms that orchestrate angiogenesis and vessel maturation have been widely studied, with signaling crosstalk between endothelium and perivascular cells being identified as an essential component. In disease, however, new vessels develop abnormally, and existing vessels lose their specialization and function, which invariably contributes to disease progression. Despite considerable research into the vasculopathic mechanisms in disease, our knowledge remains incomplete. Accordingly, the identification of angiocrine and angiopathic molecules secreted by cells within the vascular microenvironment, and their effect on vessel behaviour, remains a major research objective. Over the last decade the secreted glycoprotein leucine-rich α-2 glycoprotein 1 (LRG1), has emerged as a significant vasculopathic molecule, stimulating defective angiogenesis, and destabilizing the existing vasculature mainly, but not uniquely, by altering both canonical and non-canonical TGF-β signaling in a highly cell and context dependent manner. Whilst LRG1 does not possess any overt homeostatic role in vessel development and maintenance, growing evidence provides a compelling case for LRG1 playing a pleiotropic role in disrupting the vasculature in many disease settings. Thus, LRG1 has now been reported to damage vessels in various disorders including cancer, diabetes, chronic kidney disease, ocular disease, and lung disease and the signaling processes that drive this dysfunction are being defined. Moreover, therapeutic targeting of LRG1 has been widely proposed to re-establish a quiescent endothelium and normalized vasculature. In this review, we consider the current status of our understanding of the role of LRG1 in vascular pathology, and its potential as a therapeutic target.

Fibrosis in Chronic Kidney Disease: Pathophysiology and Therapeutic Targets

Chronic kidney disease (CKD) is a slowly progressive condition characterized by decreased kidney function, tubular injury, oxidative stress, and inflammation. CKD is a leading global health burden that is asymptomatic in early stages but can ultimately cause kidney failure. Its etiology is complex and involves dysregulated signaling pathways that lead to fibrosis. Transforming growth factor (TGF)-β is a central mediator in promoting transdifferentiation of polarized renal tubular epithelial cells into mesenchymal cells, resulting in irreversible kidney injury. While current therapies are limited, the search for more effective diagnostic and treatment modalities is intensive. Although biopsy with histology is the most accurate method of diagnosis and staging, imaging techniques such as diffusion-weighted magnetic resonance imaging and shear wave elastography ultrasound are less invasive ways to stage fibrosis. Current therapies such as renin-angiotensin blockers, mineralocorticoid receptor antagonists, and sodium/glucose cotransporter 2 inhibitors aim to delay progression. Newer antifibrotic agents that suppress the downstream inflammatory mediators involved in the fibrotic process are in clinical trials, and potential therapeutic targets that interfere with TGF-β signaling are being explored. Small interfering RNAs and stem cell-based therapeutics are also being evaluated. Further research and clinical studies are necessary in order to avoid dialysis and kidney transplantation.

Recent Advances in the Management of Diabetic Kidney Disease: Slowing Progression

Diabetic kidney disease (DKD) is a major cause of chronic kidney disease (CKD), and it heightens the risk of cardiovascular incidents. The pathogenesis of DKD is thought to involve hemodynamic, inflammatory, and metabolic factors that converge on the fibrotic pathway. Genetic predisposition and unhealthy lifestyle practices both play a significant role in the development and progression of DKD. In spite of the recent emergence of angiotensin receptors blockers (ARBs)/angiotensin converting enzyme inhibitor (ACEI), sodium-glucose cotransporter 2 (SGLT2) inhibitors, and nonsteroidal mineralocorticoid receptors antagonists (NS-MRAs), current therapies still fail to effectively arrest the progression of DKD. Glucagon-like peptide 1 receptor agonists (GLP-1RAs), a promising class of agents, possess the potential to act as renal protectors, effectively slowing the progression of DKD. Other agents, including pentoxifylline (PTF), selonsertib, and baricitinib hold great promise as potential therapies for DKD due to their anti-inflammatory and antifibrotic properties. Multidisciplinary treatment, encompassing lifestyle modifications and drug therapy, can effectively decelerate the progression of DKD. Based on the treatment of heart failure, it is recommended to use multiple drugs in combination rather than a single-use drug for the treatment of DKD. Unearthing the mechanisms underlying DKD is urgent to optimize the management of DKD. Inflammatory and fibrotic factors (including IL-1, MCP-1, MMP-9, CTGF, TNF-a and TGF-β1), along with lncRNAs, not only serve as diagnostic biomarkers, but also hold promise as therapeutic targets. In this review, we delve into the potential mechanisms and the current therapies of DKD. We also explore the additional value of combing these therapies to develop novel treatment strategies. Drawing from the current understanding of DKD pathogenesis, we propose HIF inhibitors, AGE inhibitors, and epigenetic modifications as promising therapeutic targets for the future.

Lrg1 silencing attenuates ischemia-reperfusion renal injury by regulating autophagy and apoptosis through the TGFβ1- Smad1/5 signaling pathway

BACKGROUND

Dysfunction in the processes of autophagy and apoptosis within renal tubular epithelial cells (RTEc) contributes to renal ischemia-reperfusion injury (IRI). However, the factors influencing this dysfunction remain unclear. Leucine-rich alpha-2-glycoprotein 1 (Lrg1) plays a role in the progression of diabetic nephropathy and kidney fibrosis by modulating the activin receptor-like kinase 1 (ALK1)-Smad1/5/8 and TGF-β1/Smad3 pathways, respectively. Therefore, we aimed to investigate whether Lrg1 is involved in the pathological mechanisms of renal IRI and whether its effects are related to the dysregulation of autophagy and apoptosis in RTEc.

METHODS

We conducted in vitro and in vivo experiments using CoCl2-induced hypoxic human kidney-2 (HK-2) cells and mice with renal IRI, respectively. Lrg1 was silenced using siRNA and lentiviral vectors in HK-2 cells and mouse kidneys. Rapamycin (Rapa) and methyladenine were applied to regulate autophagy in renal IRI models.

RESULTS

Increased Lrg1 expression was observed in hypoxic HK-2 cells and in the kidneys of mice with renal IRI. Silencing of Lrg1 through siRNA and lentiviral approaches restored autophagy and suppressed apoptosis in CoCl2-induced hypoxic HK-2 cells and renal IRI models. Additionally, reduced Lrg1 expression alleviated kidney damage caused by renal IRI. The downregulation of Lrg1 expression restrained the TGFβ-Smad1/5 signaling pathway in hypoxic-induced HK-2 cells and renal IRI by reducing ALK1 expression. Lastly, the enhancement of autophagy, achieved through Rapa treatment, provided protection against renal IRI in mice.

CONCLUSIONS

Our findings suggest that Lrg1 silencing can be applied as a potential therapeutic target to inhibit the TGFβ1-Smad1/5 pathway, thereby enhancing autophagy and decreasing apoptosis in patients with acute kidney injury.

Unveiling the pathogenesis and therapeutic approaches for diabetic nephropathy: insights from panvascular diseases

Diabetic nephropathy (DN) represents a significant microvascular complication in diabetes, entailing intricate molecular pathways and mechanisms associated with cardiorenal vascular diseases. Prolonged hyperglycemia induces renal endothelial dysfunction and damage via metabolic abnormalities, inflammation, and oxidative stress, thereby compromising hemodynamics. Concurrently, fibrotic and sclerotic alterations exacerbate glomerular and tubular injuries. At a macro level, reciprocal communication between the renal microvasculature and systemic circulation establishes a pernicious cycle propelling disease progression. The current management approach emphasizes rigorous control of glycemic levels and blood pressure, with renin-angiotensin system blockade conferring renoprotection. Novel antidiabetic agents exhibit renoprotective effects, potentially mediated through endothelial modulation. Nonetheless, emerging therapies present novel avenues for enhancing patient outcomes and alleviating the disease burden. A precision-based approach, coupled with a comprehensive strategy addressing global vascular risk, will be pivotal in mitigating the cardiorenal burden associated with diabetes.

The intervention of cannabinoid receptor in chronic and acute kidney disease animal models: a systematic review and meta-analysis

AIM

Cannabinoid receptors are components of the endocannabinoid system that affect various physiological functions. We aim to investigate the effect of cannabinoid receptor modulation on kidney disease.

METHODS

PubMed, Web of Science databases, and EMBASE were searched. Articles selection, data extraction and quality assessment were independently performed by two investigators. The SYRCLE's RoB tool was used to assess the risk of study bias, and pooled SMD using a random-effect model and 95% CIs were calculated. Subgroup analyses were conducted in preselected subgroups, and publication bias was evaluated. We compared the effects of CB1 and CB2 antagonists and/or knockout and agonists and/or genetic regulation on renal function, blood glucose levels, body weight, and pathological damage-related indicators in different models of chronic and acute kidney injury.

RESULTS

The blockade or knockout of CB1 could significantly reduce blood urea nitrogen [SMD,- 1.67 (95% CI - 2.27 to - 1.07)], serum creatinine [SMD, - 1.88 (95% CI - 2.91 to - 0.85)], and albuminuria [SMD, - 1.60 (95% CI - 2.16 to - 1.04)] in renal dysfunction animals compared with the control group. The activation of CB2 group could significantly reduce serum creatinine [SMD, - 0.97 (95% CI - 1.83 to - 0.11)] and albuminuria [SMD, - 2.43 (95% CI - 4.63 to - 0.23)] in renal dysfunction animals compared with the control group.

CONCLUSIONS

The results suggest that targeting cannabinoid receptors, particularly CB1 antagonists and CB2 agonists, can improve kidney function and reduce inflammatory responses, exerting a renal protective effect and maintaining therapeutic potential in various types of kidney disease.

Engineered extracellular vesicle-encapsulated CHIP as novel nanotherapeutics for treatment of renal fibrosis

Renal interstitial fibrosis (RIF) is a fundamental pathological feature of chronic kidney disease (CKD). However, toxicity and poor renal enrichment of fibrosis inhibitors limit their further applications. In this study, a platform for CKD therapy is developed using superparamagnetic iron oxide nanoparticles (SPION) decorated mesenchymal stem cells derived extracellular vesicles with carboxyl terminus of Hsc70-interacting protein (CHIP) high expression (SPION-EVs) to achieve higher renal-targeting antifibrotic therapeutic effect. SPION-EVs selectively accumulate at the injury renal sites under an external magnetic field. Moreover, SPION-EVs deliver CHIP to induce Smad2/3 degradation in renal tubular cells which alleviates Smad2/3 activation-mediated fibrosis-like changes and collagen deposition. The extracellular vesicle engineering technology provides a potential nanoplatform for RIF therapy through CHIP-mediated Smad2/3 degradation.

HIF-1α: A potential therapeutic opportunity in renal fibrosis

Renal fibrosis is a common outcome of various renal injuries, leading to structural destruction and functional decline of the kidney, and is also a critical prognostic indicator and determinant in renal diseases therapy. Hypoxia is induced in different stress and injuries in kidney, and the hypoxia inducible factors (HIFs) are activated in the context of hypoxia in response and regulation the hypoxia in time. Under stress and hypoxia conditions, HIF-1α increases rapidly and regulates intracellular energy metabolism, cell proliferation, apoptosis, and inflammation. Through reprogramming cellular metabolism, HIF-1α can directly or indirectly induce abnormal accumulation of metabolites, changes in cellular epigenetic modifications, and activation of fibrotic signals. HIF-1α protein expression and activity are regulated by various posttranslational modifications. The drugs targeting HIF-1α can regulate the downstream cascade signals by inhibiting HIF-1α activity or promoting its degradation. As the renal fibrosis is affected by renal diseases, different diseases may trigger different mechanisms which will affect the therapy effect. Therefore, comprehensive analysis of the role and contribution of HIF-1α in occurrence and progression of renal fibrosis, and determination the appropriate intervention time of HIF-1α in the process of renal fibrosis are important ideas to explore effective treatment strategies. This study reviews the regulation of HIF-1α and its mediated complex cascade reactions in renal fibrosis, and lists some drugs targeting HIF-1α that used in preclinical studies, to provide new insight for the study of the renal fibrosis mechanism.

Leucine-Rich Alpha-2 Glycoprotein 1 Accumulates in Complicated Atherosclerosis and Promotes Calcification

Atherosclerosis is the primary cause of cardiovascular disease. The development of plaque complications, such as calcification and neo-angiogenesis, strongly impacts plaque stability and is a good predictor of mortality in patients with atherosclerosis. Despite well-known risk factors of plaque complications, such as diabetes mellitus and chronic kidney disease, the mechanisms involved are not fully understood. We and others have identified that the concentration of circulating leucine-rich α-2 glycoprotein 1 (LRG1) was increased in diabetic and chronic kidney disease patients. Using apolipoprotein E knockout mice (ApoE-/-) (fed with Western diet) that developed advanced atherosclerosis and using human carotid endarterectomy, we showed that LRG1 accumulated into an atherosclerotic plaque, preferentially in calcified areas. We then investigated the possible origin of LRG1 and its functions on vascular cells and found that LRG1 expression was specifically enhanced in endothelial cells via inflammatory mediators and not in vascular smooth muscle cells (VSMC). Moreover, we identified that LRG1 was able to induce calcification and SMAD1/5-signaling pathways in VSMC. In conclusion, our results identified for the first time that LRG1 is a direct contributor to vascular calcification and suggest a role of this molecule in the development of plaque complications in patients with atherosclerosis.

Relationship between plasma leucine-rich α-2-glycoprotein 1 and urinary albumin excretion in patients with type 2 diabetes

Aims

To explore the relationship between plasma leucine-rich α-2-glycoprotein 1 (LRG1) level and the degree of urinary albumin excretion in patients with type 2 diabetes.

Methods

We evaluated 332 patients with type 2 diabetes in a cross-sectional study.

Result

The plasma LRG1 level differed significantly according to the quartiles of urinary albumin excretion (Q1 [<7.7 mg/g], 17.1 μg/mL; Q2 [7.7-15.0 mg/g], 17.5 μg/mL; Q3 [15.1-61.4 mg/g], 18.6 μg/mL; Q4 [≥61.5 mg/g], 22.3 μg/mL; p for trend = 0.003) under adjustment with other covariates. A positive correlation was found between plasma LRG1 level and urinary albumin excretion (ρ = 0.256, p <0.001). According to a multivariate model, the association between LRG1 and urinary albumin excretion remained significant, under adjustment for confounding factors (β = 0.285, p <0.001).

Conclusion

Plasma LRG1 level was independently associated with urinary albumin excretion in patients with type 2 diabetes. This study suggests that LRG1 may be associated with increased excretion of urinary albumin in the early stages of diabetic nephropathy.

Cellular crosstalk of mesangial cells and tubular epithelial cells in diabetic kidney disease

Diabetic kidney disease (DKD) is a major cause of end-stage renal disease and imposes a heavy global economic burden; however, little is known about its complicated pathophysiology. Investigating the cellular crosstalk involved in DKD is a promising avenue for gaining a better understanding of its pathogenesis. Nonetheless, the cellular crosstalk of podocytes and endothelial cells in DKD is better understood than that of mesangial cells (MCs) and renal tubular epithelial cells (TECs). As the significance of MCs and TECs in DKD pathophysiology has recently become more apparent, we reviewed the existing literature on the cellular crosstalk of MCs and TECs in the context of DKD to acquire a comprehensive understanding of their cellular communication. Insights into the complicated mechanisms underlying the pathophysiology of DKD would improve its early detection, care, and prognosis. Video Abstract.

TP53RK Drives the Progression of Chronic Kidney Disease by Phosphorylating Birc5

Renal fibrosis is a common characteristic of various chronic kidney diseases (CKDs) driving the loss of renal function. During this pathological process, persistent injury to renal tubular epithelial cells and activation of fibroblasts chiefly determine the extent of renal fibrosis. In this study, the role of tumor protein 53 regulating kinase (TP53RK) in the pathogenesis of renal fibrosis and its underlying mechanisms is investigated. TP53RK is upregulated in fibrotic human and animal kidneys with a positive correlation to kidney dysfunction and fibrotic markers. Interestingly, specific deletion of TP53RK either in renal tubule or in fibroblasts in mice can mitigate renal fibrosis in CKD models. Mechanistic investigations reveal that TP53RK phosphorylates baculoviral IAP repeat containing 5 (Birc5) and facilitates its nuclear translocation; enhanced Birc5 displays a profibrotic effect possibly via activating PI3K/Akt and MAPK pathways. Moreover, pharmacologically inhibiting TP53RK and Birc5 using fusidic acid (an FDA-approved antibiotic) and YM-155(currently in clinical phase 2 trials) respectively both ameliorate kidney fibrosis. These findings demonstrate that activated TP53RK/Birc5 signaling in renal tubular cells and fibroblasts alters cellular phenotypes and drives CKD progression. A genetic or pharmacological blockade of this axis serves as a potential strategy for treating CKDs.

LRG1 Promotes ECM Integrity by Activating the TGF-β Signaling Pathway in Fibroblasts

Leucine-rich alpha-2-glycoprotein 1 (LRG1) mediates skin repair and fibrosis by stimulating the transforming growth factor-beta (TGF-β) signaling pathway. In the present study, we investigated the effect of LRG1 on extracellular matrix (ECM) integrity in fibroblasts, as well as on skin aging. The treatment of dermal fibroblasts with purified recombinant human LRG1 increased type I collagen secretion and decreased matrix metalloproteinase-1 secretion. Additionally, LRG1 promoted SMAD2/SMAD3 phosphorylation in a pattern similar to that of TGF-β1 treatment. An inhibitor of TGF-β receptor 1 abolished LRG1-induced SMAD2 phosphorylation. RNA sequencing identified "extracellular region", "extracellular space", and "extracellular matrix" as the main Gene Ontology terms in the differentially expressed genes of fibroblasts treated with or without LRG1. LRG1 increased TGF-β1 mRNA levels, suggesting that LRG1 partially transactivates the expression of TGF-β1. Furthermore, an increased expression of type I collagen was also observed in fibroblasts grown in three-dimensional cultures on a collagen gel mimicking the dermis. LRG1 mRNA and protein levels were significantly reduced in elderly human skin tissues with weakened ECM integrity compared to in young human skin tissues. Taken together, our results suggest that LRG1 could retard skin aging by activating the TGF-β signaling pathway, increasing ECM deposition while decreasing its degradation.

Genetic and pharmacological inhibition of METTL3 alleviates renal fibrosis by reducing EVL m6A modification through an IGF2BP2-dependent mechanism

BACKGROUND

N6 -methyladenosine (m6A) is of great importance in renal physiology and disease progression, but its function and mechanism in renal fibrosis remain to be comprehensively and extensively explored. Hence, this study will explore the function and potential mechanism of critical regulator-mediated m6A modification during renal fibrosis and thereby explore promising anti-renal fibrosis agents.

METHODS

Renal tissues from humans and mice as well as HK-2 cells were used as research subjects. The profiles of m6A modification and regulators in renal fibrosis were analysed at the protein and RNA levels using Western blotting, quantitative real-time polymerase chain reaction and other methods. Methylation RNA immunoprecipitation sequencing and RNA sequencing coupled with methyltransferase-like 3 (METTL3) conditional knockout were used to explore the function of METTL3 and potential targets. Gene silencing and overexpression combined with RNA immunoprecipitation were performed to investigate the underlying mechanism by which METTL3 regulates the Ena/VASP-like (EVL) m6A modification that promotes renal fibrosis. Molecular docking and virtual screening with in vitro and in vivo experiments were applied to screen promising traditional Chinese medicine (TCM) monomers and explore their mechanism of regulating the METTL3/EVL m6A axis and anti-renal fibrosis.

RESULTS

METTL3 and m6A modifications were hyperactivated in both the tubular region of fibrotic kidneys and HK-2 cells. Upregulated METTL3 enhanced the m6A modification of EVL mRNA to improve its stability and expression in an insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2)-dependent manner. Highly expressed EVL binding to Smad7 abrogated the Smad7-induced suppression of transforming growth factor-β (TGF-β1)/Smad3 signal transduction, which conversely facilitated renal fibrosis progression. Molecular docking and virtual screening based on the structure of METTL3 identified a TCM monomer named isoforsythiaside, which inhibited METTL3 activity together with the METTL3/EVL m6A axis to exert anti-renal fibrosis effects.

CONCLUSIONS

Collectively, the overactivated METTL3/EVL m6A axis is a potential target for renal fibrosis therapy, and the pharmacological inhibition of METTL3 activity by isoforsythiaside suggests that it is a promising anti-renal fibrosis agent.

Oxidative stress and inflammation in diabetic nephropathy: role of polyphenols

Diabetic nephropathy (DN) often leads to end-stage renal disease. Oxidative stress demonstrates a crucial act in the onset and progression of DN, which triggers various pathological processes while promoting the activation of inflammation and forming a vicious oxidative stress-inflammation cycle that induces podocyte injury, extracellular matrix accumulation, glomerulosclerosis, epithelial-mesenchymal transition, renal tubular atrophy, and proteinuria. Conventional treatments for DN have limited efficacy. Polyphenols, as antioxidants, are widely used in DN with multiple targets and fewer adverse effects. This review reveals the oxidative stress and oxidative stress-associated inflammation in DN that led to pathological damage to renal cells, including podocytes, endothelial cells, mesangial cells, and renal tubular epithelial cells. It demonstrates the potent antioxidant and anti-inflammatory properties by targeting Nrf2, SIRT1, HMGB1, NF-κB, and NLRP3 of polyphenols, including quercetin, resveratrol, curcumin, and phenolic acid. However, there remains a long way to a comprehensive understanding of molecular mechanisms and applications for the clinical therapy of polyphenols.

Expression of LRG-1 in mice with hypertensive renal damage and its significance

OBJECTIVES

Long-term elevated blood pressure may lead to kidney damage, yet the pathogenesis of hypertensive kidney damage is still unclear. This study aims to explore the role and significance of leucine-rich alpha-2-glycoprotein-1 (LRG-1) in hypertensive renal damage through detecting the levels of LRG-1 in the serum and kidney of mice with hypertensive renal damage and its relationship with related indexes.

METHODS

C57BL/6 mice were used in this study and randomly divided into a control group, an angiotensin II (Ang II) group, and an Ang II+irbesartan group. The control group was gavaged with physiological saline. The Ang II group was pumped subcutaneously at a rate of 1.5 mg/(kg·d) for 28 days to establish the hypertensive renal damage model in mice, and then gavaged with equivalent physiological saline. The Ang II+irbesartan group used the same method to establish the hypertensive renal damage model, and then was gavaged with irbesartan. Immunohistochemistry and Western blotting were used to detect the expression of LRG-1 and fibrosis-related indicators (collagen I and fibronectin) in renal tissues. ELISA was used to evaluate the level of serum LRG-1 and inflammatory cytokines in mice. The urinary protein-creatinine ratio and renal function were determined, and correlation analysis was conducted.

RESULTS

Compared with the control group, the levels of serum LRG-1, the expression of LRG-1 protein, collagen I, and fibronectin in kidney in the Ang II group were increased (all P<0.01). After treating with irbesartan, renal damage of hypertensive mice was alleviated, while the levels of LRG-1 in serum and kidney were decreased, and the expression of collagen I and fibronectin was down-regulated (all P<0.01). Correlation analysis showed that the level of serum LRG-1 was positively correlated with urinary protein-creatinine ratio, blood urea nitrogen, and blood creatinine level in hypertensive kidney damage mice. Serum level of LRG-1 was also positively correlated with serum inflammatory factors including TNF-α, IL-1β, and IL-6.

CONCLUSIONS

Hypertensive renal damage mice display elevated expression of LRG-1 in serum and kidney, and irbesartan can reduce the expression of LRG-1 while alleviating renal damage. The level of serum LRG-1 is positively correlated with the degree of hypertensive renal damage, suggesting that it may participate in the occurrence and development of hypertensive renal damage.

TSLP/TSLPR promotes renal fibrosis by activating STAT3 in renal fibroblasts

Previous studies have demonstrated the importance of TSLP-TSLPR in inflammatory, allergic, and fibrotic diseases. However, their exact molecular mechanism in regulating renal fibrosis has not been fully explored yet. The current study identified the high expression levels of TSLP and TSLPR in human and mouse hydronephrotic tissues. In addition, immunofluorescence staining showed that TSLP was highly expressed in renal tubular cells, while TSLPR was mainly co-localized with α-SMA, a marker of fibroblasts. Knocking out TSLPR in the UUO model could alleviate the severity of renal fibrosis. Most importantly, the application of antibody blockade of TSLP reduced the fibrotic level in the UUO model. The functional analysis revealed that the hypoxic exposure could induce the overexpression of TSLP in renal tubular cells via HIF-1α. The tubular cell-derived TSLP could bind to the TSLPR of fibroblasts in a paracrine manner to activate them. Specifically, the HIF-1α/TSLP/TSLPR-axis could activate fibroblasts through the STAT3 signaling pathway. This study revealed a mechanistic interaction of HIF-1α/TSLP/TSLPR and STAT3 signaling pathways in the activation and proliferation of human and murine kidney fibroblasts; these pathways might be exploited as a therapeutic target in renal fibrosis.

Tartary buckwheat flavonoids alleviates high-fat diet induced kidney fibrosis in mice by inhibiting MAPK and TGF-β1/Smad signaling pathway

Tartary buckwheat flavonoids (TBF) are active components extracted from Tartary buckwheat, which have abundant biological effects. According to this study, we investigated the effect of TBF on high-fat diet (HFD)-induced kidney fibrosis and its related mechanisms. In vivo, we established an HFD-induced kidney fibrosis model in mice and administered TBF. The results showed that TBF was able to alleviate kidney injury and inflammatory response. Subsequently, the mRNA levels between the HFD group and the TBF + HFD group were detected using RNA-seq assay. According to the gene set enrichment analysis (GSEA) and Kyoto Encyclopedia of Genes and Genomes (KEGG) results, the differential genes were enriched in lipid metabolism and mitogen-activated protein kinases(MAPK) signaling pathways. We examined the protein expression of lipid metabolism-related pathways and the level of lipid metabolism. The results showed that TBF significantly activated the adenosine monophosphate activated protein kinase/acetyl-CoA carboxylase (AMPK/ACC) pathway and effectively reduced kidney total cholesterol (TC), triglyceride (TG) and low-density lipoproteinc cholesterol (LDL-C) levels and increased high-density lipoprotein cholesterol (HDL-C) levels in mice. TBF also inhibited transforming growth factor-β1/Smad (TGF-β1/Smad) and MAPK signaling pathways, thus slowing down the kidney fibrosis process. In vitro, using palmitic acid (PA) to stimulate TCMK-1 cells, the in vivo results similarly demonstrated that TBF could alleviate kidney fibrosis in HFD mice by inhibiting TGF1/Smad signaling pathway and MAPK signaling pathway.

Identification and validation of immune-related biomarkers and potential regulators and therapeutic targets for diabetic kidney disease

BACKGROUND

Diabetic kidney disease (DKD) is a major complication of diabetes and the leading cause of end-stage renal disease worldwide. Renal inflammation and infiltration of immune cells contribute to the development and progression of DKD. Thus, the aim of the present study was to identify and validate immune-related biomarkers and analyze potential regulators including transcription factors (TFs), microRNAs (miRNAs), and drugs for DKD.

METHODS

Immune-related genes from the ImmPort database and glomeruli samples from GSE1009 and GSE30528 were used to identify differentially expressed immune-related genes (DEIRGs) of DKD. The expression level and clinical correlation analyses of DEIRGs were verified in the Nephroseq database. Murine podocytes were cultured to construct the high glucose-induced podocyte injury model. The reliability of the bioinformatics analysis was experimentally validated by RT-qPCR in podocytes. Networks among DEIRGs, regulators, and drugs were constructed to predict potential regulatory mechanisms for DKD.

RESULTS

DKD-associated DEIRGs were identified. CCL19 and IL7R were significantly upregulated in the DKD group and negatively correlated with glomerular filtration rate (GFR). GHR, FGF1, FYN, VEGFA, F2R, TGFBR3, PTGDS, FGF9, and SEMA5A were significantly decreased in the DKD group and positively correlated with GFR. RT-qPCR showed that the relative mRNA expression levels of GHR, FGF1, FYN, TGFBR3, PTGDS, FGF9, and SEMA5A were significantly down-regulated in the high glucose-induced podocyte injury group. The enriched regulators for DEIRGs included 110 miRNAs and 8 TFs. The abnormal expression of DEIRGs could be regulated by 16 established drugs.

CONCLUSIONS

This study identified immune-related biomarkers, regulators, and drugs of DKD. The findings of the present study provide novel insights into immune-related diagnosis and treatment of DKD.

Kidney fibrosis: from mechanisms to therapeutic medicines

Chronic kidney disease (CKD) is estimated to affect 10-14% of global population. Kidney fibrosis, characterized by excessive extracellular matrix deposition leading to scarring, is a hallmark manifestation in different progressive CKD; However, at present no antifibrotic therapies against CKD exist. Kidney fibrosis is identified by tubule atrophy, interstitial chronic inflammation and fibrogenesis, glomerulosclerosis, and vascular rarefaction. Fibrotic niche, where organ fibrosis initiates, is a complex interplay between injured parenchyma (like tubular cells) and multiple non-parenchymal cell lineages (immune and mesenchymal cells) located spatially within scarring areas. Although the mechanisms of kidney fibrosis are complicated due to the kinds of cells involved, with the help of single-cell technology, many key questions have been explored, such as what kind of renal tubules are profibrotic, where myofibroblasts originate, which immune cells are involved, and how cells communicate with each other. In addition, genetics and epigenetics are deeper mechanisms that regulate kidney fibrosis. And the reversible nature of epigenetic changes including DNA methylation, RNA interference, and chromatin remodeling, gives an opportunity to stop or reverse kidney fibrosis by therapeutic strategies. More marketed (e.g., RAS blockage, SGLT2 inhibitors) have been developed to delay CKD progression in recent years. Furthermore, a better understanding of renal fibrosis is also favored to discover biomarkers of fibrotic injury. In the review, we update recent advances in the mechanism of renal fibrosis and summarize novel biomarkers and antifibrotic treatment for CKD.

Urine Leucine-Rich α-2 Glycoprotein 1 (LRG1) Predicts the Risk of Progression to End-Stage Kidney Disease in Patients With Type 2 Diabetes

OBJECTIVE

Leucine-rich α-2 glycoprotein 1 (LRG1) was recently identified as an amplifier of transforming growth factor-β (TGF-β)-induced kidney fibrosis in animal models. We aimed to study whether urine LRG1 is associated with risk of progression to end-stage kidney disease (ESKD) in individuals with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 1,837 participants with type 2 diabetes and estimated glomerular filtration rate (eGFR) >30 mL/min/1.73 m2 were recruited from a regional hospital and a primary care facility. Association of urine LRG1 with risk of ESKD (progression to sustained eGFR <15 mL/min/1.73 m2, dialysis, or death resulting from renal causes) was assessed by survival analyses.

RESULTS

During a median follow-up of 8.6 (interquartile range 5.8-9.6) years, 134 incident ESKD events were identified. Compared with those in the lowest tertile, participants with baseline urine LRG1 in the highest tertile had a 1.91-fold (95% CI 1.04-3.50) increased risk of progression to ESKD, after adjustment for cardiorenal risk factors, including eGFR and albuminuria. As a continuous variable, 1 SD increment in urine LRG1 was associated with a 1.53-fold (95% CI 1.19-1.98) adjusted risk of ESKD. Of note, the association of urine LRG1 with ESKD was independent of plasma LRG1. Moreover, urine LRG1 was associated with rapid kidney function decline and progression to macroalbuminuria, two common pathways leading to ESKD.

CONCLUSIONS

Urine LRG1, a TGF-β signaling modulator, predicts risk of progression to ESKD independently of clinical risk factors in patients with type 2 diabetes, suggesting that it may be a novel factor involved in the pathophysiological pathway leading to kidney disease progression.

Sestrin2 Signaling Pathway Regulates Podocyte Biology and Protects against Diabetic Nephropathy

Sestrin2 regulates cell homeostasis and is an upstream signaling molecule for several signaling pathways. Sestrin2 leads to AMP-activated protein kinase- (AMPK-) and GTPase-activating protein activity toward Rags (GATOR) 1-mediated inhibition of mammalian target of rapamycin complex 1 (mTORC1), thereby enhancing autophagy. Sestrin2 also improves mitochondrial biogenesis via AMPK/Sirt1/peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) signaling pathway. Blockade of ribosomal protein synthesis and augmentation of autophagy by Sestrin2 can prevent misfolded protein accumulation and attenuate endoplasmic reticulum (ER) stress. In addition, Sestrin2 enhances P62-mediated autophagic degradation of Keap1 to release nuclear factor erythroid 2-related factor 2 (Nrf2). Nrf2 release by Sestrin2 vigorously potentiates antioxidant defense in diabetic nephropathy. Impaired autophagy and mitochondrial biogenesis, severe oxidative stress, and ER stress are all deeply involved in the development and progression of diabetic nephropathy. It has been shown that Sestrin2 expression is lower in the kidney of animals and patients with diabetic nephropathy. Sestrin2 knockdown aggravated diabetic nephropathy in animal models. In contrast, upregulation of Sestrin2 enhanced autophagy, mitophagy, and mitochondrial biogenesis and suppressed oxidative stress, ER stress, and apoptosis in diabetic nephropathy. Consistently, overexpression of Sestrin2 ameliorated podocyte injury, mesangial proliferation, proteinuria, and renal fibrosis in animal models of diabetic nephropathy. By suppressing transforming growth factor beta (TGF-β)/Smad and Yes-associated protein (YAP)/transcription enhancer factor 1 (TEF1) signaling pathways in experimental models, Sestrin2 hindered epithelial-mesenchymal transition and extracellular matrix accumulation in diabetic kidneys. Moreover, modulation of the downstream molecules of Sestrin2, for instance, augmentation of AMPK or Nrf2 signaling and inhibition of mTORC1, has been protective in diabetic nephropathy. Regarding the beneficial effects of Sestrin2 on diabetic nephropathy and its interaction with several signaling molecules, it is worth targeting Sestrin2 in diabetic nephropathy.